A polycarbonate (hereinafter, may be called as PC) resin consisting of an aromatic polycarbonate unit and an aliphatic polyether unit has been known as a resin having an excellent property in toughness. For example, a method has been disclosed for copolymerizing a phenol-modified diol (diester diol) which is used as a co-monomer and is derived from p-hydroxybenzoic acid or its alkylester or an acid chloride and a diol (for example, refer to Patent Document 1). Specifically, a PC copolymer has been proposed, which is obtained by copolymerizing a co-monomer of tetramethylene glycol (molecular weight: 2,000)-bis(4-hydroxybenzoate) or polyethylene glycol (molecular weight: 8,000)-bis(4-hydroxybenzoate). The PC copolymer using these diester diols can be produced by conventional interfacial polymerization, however, the following problems have been encountered: a PC copolymer with high purity is not easy to obtain because in the washing step of polymerization solution the methylene chloride phase which contains the PC copolymer is poorly separated from the water phase which contains impurities; and productivity is lowered greatly when a PC copolymer with high purity is tried to be obtained.
In order to avoid the above problems, in the specification of Japanese Patent Application No. 2004-04293, the present applicant had proposed a method for producing a polycarbonate copolymer, where separation of the water phase from the methylene chloride phase after polymerization is improved by using a co-monomer which contains 500 ppm by mass or less of a hydroxybenzoic acid. However, separation of the PC copolymer in an acid- or water-washing process after polymerization is not necessarily satisfied, so that a still improved method has been requested.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. Shou62-79222.